Persons skilled in the construction field will be familiar with the fact that sound safety practice requires that all current carrying cable and other types of wire be installed in appropriately sized conduit which, for example, may be arranged to interconnect service entrance box and distribution box centers.
Typical construction procedure requires that the service entrance and distribution box centers, the interconnecting conduit and like be placed in a new building at an early stage in the construction thereof. At this point in such construction the boxes and conduit are empty, inasmuch as the electrical and other types of conductors are to be installed at a later stage of the construction. In large commercial and industrial buildings, the conduit employed may be required to have a diameter of one-half inch to approximately four inches, and when installed will be bent at various angles, offset, elbowed or the like.
The conductors employed in conduit of the sizes here under consideration frequently have nominal diameters of half an inch or less. Material economy dictates that as many conductors as possible be placed in each conduit, which conduit may be of a diameter ranging from one-half inch to one and one-half inches. The length of conduit run obviously varies, with the lengths depending upon the physical features of the building, and runs of several hundred feet are not uncommon.
Long runs of wire are frequently utilized when, for example, wiring is to be installed for the tall lights used to illuminate large parking lots. These facts, namely, the length and often erratic path of the conduit run, and the size and number of conductors placed in each conduit, make the job of pulling the conductors through such conduit an extremely difficult one, unless some manually powered or electrically powered wire puller is utilized.
To better understand the instant invention, brief consideration should be given to the procedure followed in conductor installation. Initially, a very light lead line is fed through the conduit run. This may be accomplished by first shooting a small jet line with a string through the conduit. Compressed air is usually employed for this purpose. The lead line is then connected to a cable or pull rope (nylon or plastic) which is fed through the run. A mechanical connection is then provided between the cable or rope and the conductors. The cable or rope and the connected conductors are then pulled through the conduit. Recently, pipes of polyvinyl chloride (p.v.c.) or of aluminum have been employed for use as conduits, inasmuch as p.v.c. and aluminum have the advantage of light weight, resistance to deterioration during long periods underground, and in addition, these are relatively easy to install. With conduit of p.v.c. or aluminum, a rope pull line is far more desirable than a steel cable, for the steel cable tends to gouge the relatively soft interiors of these types of conduit.
Problems and difficulties have been encountered when employing such force multiplying devices on small pull ropes, which stem largely from the fact that the pulling force may exceed the tensile strength of the pull line, which will suddenly sever or break the pull line. Such an occurrence may well result in injury to nearby operators or damage to property.
To develop the pulling force required, prior art practice has dictated that a wide variety of force multiplying devices be used. For example, block and tackle, windlass and powered winches have in the past been employed. Because of the wide difference of the physical features of each installation, the equipment referred to above was usually specially rigged for each job. Set up time alone, therefore, represented an important cost factor for each job. Frequently, set up time could not even be estimated accurately before the job was actually begun. In many cases, special temporary scaffolding would have to be built before conductor pulling could commence.
Commercial machines utilized for pulling large diameter wire cost a minimum of $3,000 to $5,000.00 and weigh in the vicinity of three hundred pounds, which of course means that one person cannot alone operate a machine. Consequently, when #6 wire or similar size is being dealt with, there has been a tendency to move in the direction of using hand operated devices, which usually can be operated by one person. Most of such hand operated devices, however, have used a crank and pulley arrangement, in the nature of a winch. Unfortunately, such a device can only accommodate a finite length of cable, typically two hundred feet or less, so in the event that wiring is to be installed underground in a large parking lot, for example, where considerable distances between light poles are involved, such a prior art device cannot be used.
Therefore, it is to be seen that a long standing need has existed for light duty wire puller which provides pulling power with an extra measure of safety in pulling smaller size conductors.